Why can a hearing test show that your threshold of hearing is 0 dB at 250 Hz, when Figure 17.37 implies that no one can hear such a frequency at less than
NIB - Test Tone(sub-bass) - 40Hz (0db) Sine Wave - YouTube
How to set amplifier gain using test tones
40 Hz Test Tone by Fred & Sound (Subwoofer adjustment) - YouTube